An antenna is a conductor or system of conductors designed to radiate or intercept electromagnetic waves. While being varied in size and shape, all antennas are made up of conducting material and require a feed system to extract or accept energy. An antenna converts guided electric waves into electromagnetic waves in free space. A matching device of some sort is generally employed to facilitate this conversion, and a transmission line is often used to efficiently guide the electric waves from the transmitter to the antenna.
Antennas employing parabolic reflectors have been in widespread use for many years to direct the wave front to the receiver in phase. This is accomplished by the geometry of the parabolic reflector which provides a constant path length from any point on the reference plane to the receiver. Basically, waves arriving at the reflector surface in phase are reflected to the focal point along equi-distant paths, thereby arriving at the focal point in phase.
Because of the resulting high gain, the constant path length parabolic antenna is popular for use at many wavelengths, including microwave and visible. For a satellite receiving station, the diameter of the parabola is a function of the merit factor, G/T, linking the gain G of the parabola and the overall noise temperature (T) desired on the station. Generally, the diameter of the parabola defines its beam width. At the same time, the beam width determines the sensitivity of the system to interference coming from satellites adjacent to the satellite aimed at, which limits the ability to reduce the diameter of the parabola.
The packaging, deployment, size and pointing difficulties for employing a conventional parabola make it impractical for use in space as well as in other applications.
Flat array antennas are being used to overcome the limits imposed by parabolic designs. In an array antenna, an array of receiving elements are arranged in parallel, and the gain is a function of the area of the antenna. However, for flat array antennas employing summing systems, efficiency decreases as area increases because of the loss generated in the summing systems.
An example of a flat array antenna having a summing system is described in U.S. Pat. No. 5,227,808 to Davis. The antenna array is constructed in sub-arrays which are supported in a stacked and folded condition and then expanded when deployed in space. Each sub-array includes a plurality of tapered notch antenna elements, each of which is fed by a section of slotline, which is in turn fed by a coplanar waveguide.
While electronic phasing devices used in conjunction with flat array antennas might be generally workable, they tend to be complicated, fragile and difficult to assemble.
A need exists for antennas having in excess of 10% bandwidth for high quality data transmission, which are light weight for ease of rapid pointing and are capable of high gain, while at the same time being physically thin for ease of storage and deployment and low blockage.